Optimum fuel efficiency is achieved when a combustion engine reaches an optimal operating temperature range. This is connected substantially with the friction of the moving parts, which is higher during cold start, particularly at a low ambient temperature. In addition, there is the increased viscosity of the cold engine oil, which likewise decreases only as the temperature increases. Moreover, exhaust emission figures of the combustion engine are also increased in the cold starting phase, this being attributable to the effectiveness of the exhaust gas aftertreatment devices arranged in the exhaust line, e.g., a catalytic converter, which increase as warm-up progresses.
For the reasons mentioned above, efforts in the development of combustion engines are focused on warming up as quickly as possible after cold starting. On the other hand, combustion engines may be operated within a certain temperature range. To keep within this range at the top, appropriate cooling measures are utilized. For this purpose, air cooled combustion engines have surface regions with a, generally finned, external structure in order to dissipate some of the operational heat to the ambient air via the surface area enlarged in this way. In contrast, the coolant flowing around the engine block and the cylinder head in water-cooled combustion engines absorbs a large part of the waste heat which arises. For this purpose, passages may be arranged in the housing wall of the combustion engine, forming a “coolant jacket” together with the coolant flowing through them.
Coolant is then passed through at least one suitable cooler arrangement via a self-contained cooling circuit to prevent overheating. During this process, at least some of the heat absorbed by the coolant is released to the ambient air via the cooler arrangement, which usually comprises at least one air/coolant heat exchanger.
In this way, it is possible to use the heat from the coolant, which is available in any case, to warm the vehicle interior independently of external factors as well for an engine cooling system combined with a vehicle heating system. For this purpose, a heating arrangement comprising at least one heating heat exchanger, which may be an air/coolant heat exchanger, is integrated into the cooling circuit. The operation of the vehicle heating system envisages that air is drawn in from outside and/or from the interior of the vehicle and guided past the heating heat exchanger or through the latter. During this process, the air absorbs some of the heat energy before being passed into the interior of the vehicle.
Apart from enhancing comfort in this way, however, vehicle heating systems also perform tasks associated with visibility. Above all, it is a clear view through the glazed portions of the vehicle which is at the forefront here. Thus, for example, low external temperatures have the effect that the water vapor in the interior precipitates on the windows. As a consequence, these can then become misted up or even ice over, clouding or obscuring the view.
Various embodiments of engine cooling systems in combination with vehicle heating systems are already known in the prior art. Some of these envisage a flow-free strategy, which is also referred to as a “no flow strategy”. In simple systems, the circulation of the coolant through the coolant jacket of the combustion engine is interrupted, particularly during the cold starting phase, resulting in improved—because quicker—engine warm-up. However, such strategies are not suitable for vehicle heating systems that operate using coolant, which require an inflow of heated coolant in the event of a demand for heating, which typically arises already in the cold starting phase, this in turn requiring immediate abandonment of the no flow strategy.
In order also to be able to use a no flow strategy in combination with vehicle heating systems which desire a flow of coolant, compromise solutions in the form of “split cooling systems” have become established. These provide for division of the cooling circuit. In this case, the coolant jacket of the combustion engine can be divided into a part for the engine block and a part for the cylinder head. In this way, it is possible, for example, to supply the coolant jacket of the cylinder head with flowing coolant right from the starting of the combustion engine, while the coolant flow to the coolant jacket of the engine block is advantageously still shut off (no flow strategy).
Since the cylinder head, which contains the outlets for the exhaust gas, is the quickest to warm up in any case, that part of the coolant which is warmed up by the cylinder head can already be used for the vehicle heating system. In contrast, the shut off part of the coolant jacket contributes to the ability of the engine block to warm up more quickly without losing part of the heat energy required for this purpose to the rest of the coolant, which is flowing.
Another approach to reducing fuel consumption in combustion engines having a plurality of cylinders is seen in the deactivation of at least one of said cylinders. Shutting down individual cylinders is also known as “dynamic downsizing”. The deactivation of one or more cylinders can be performed primarily in part-load operation of the combustion engine, in which only a correspondingly low power demand is required. The way in which shutdown is performed is based on the particular type of combustion engine. In addition to individual cylinder shutdown, this can take the form of deactivation of a complete cylinder bank, particularly in the case of V engines.
Systems of this kind are known from U.S. Pat. No. 7,966,978 B2 and DE 10 2008 030 422 A1, for example. These are concerned with the problem which sometimes occurs with cylinder shutdown, namely that of nonuniform temperature distribution within the combustion engine. This can occur, for example, with individual cylinders shut down over a prolonged period and can prove disadvantageous when the cylinders, which are then cold, are subsequently activated. In this case, the proposal is to separate the cylinders envisaged for possible deactivation and the cylinders envisaged for continuous operation in such a way that said cylinders are cooled by cooling water jackets that are separated from one another. Specifically, a combustion engine in the form of a V engine, the first cylinder bank of which is provided for permanently active operation and the second cylinder bank of which is provided for deactivatable operation, is disclosed. Both cylinder banks are surrounded by different cooling water jackets, wherein coolant flows only through the cooling water jacket of the first cylinder bank in the deactivated state of the second cylinder bank.
Here, the cooling water jackets of the two cylinder banks extend both around the region of the associated engine block which contains the cylinders and around the associated cylinder head of the respective cylinder bank.
In order to ensure separation between the cooling water jackets of the two cylinder banks, a bypass is provided, which allows the coolant from the cooling water jacket of the first cylinder bank to circulate through the cooling system while bypassing the second cylinder bank. In this way, more rapid warm-up of the first cylinder bank is achieved. If the shutdown of the second cylinder bank takes place during continuous operation, the bypass is closed if said bank is cooled down too much, with the result that the warm coolant from the coolant jacket of the activated first cylinder bank flows directly into the coolant jacket of the shut-down second cylinder bank and circulates onward from there. More even temperature distribution is achieved even when the second cylinder bank is deactivated.
Cylinder shutdown is based on operating the cylinder/s which is/are then still active at a higher load. Such operation is associated with improved fuel consumption, wherein, in particular, higher cylinder and/or exhaust gas temperatures are achieved.
JP 2014/015898 A likewise discloses a method for operating a combustion engine having cylinders that can be shut down. The cooling of the pistons thereof, which are arranged in the individual cylinders, is accomplished by an oil jet mechanism. If one or more cylinders are shut down, particularly in part-load operation of the combustion engine, the oil supply to the shut-down cylinder/s is simultaneously interrupted. In this way, excessive cooling of the cylinder/s which is/are still active is supposed to be prevented since otherwise some of the heat from the engine oil is lost via the regions of the combustion engine around the inactive cylinder/s.
Shutting down one cylinder or individual cylinders in combination with stopping admission to the cylinder/s which has/have been shut down allows extremely ecological and economical operation of combustion engines. Particularly the reduction of the mass to be warmed up owing to those parts through which there is no coolant flow in the shutdown phases allows rapid warm-up, from a cold start, of those regions which are active.
At the same time, complete shutdown of the cooling of the engine block and the cylinder head does not appear advisable since high temperatures, especially in the engine block, cause an advantageous reduction in friction. The warming, necessary for this purpose, in the cold starting phase is accomplished largely by means of the circulating coolant, which can in this way transfer the more rapid warm-up of the combustion chambers within the cylinder head at least partially to the engine block. It is the object of the present disclosure to achieve more rapid warm-up of the engine via more selective heating and/or cooling of the engine during cold-start.
In one example, the issues described above may be addressed by a method for deactivating a first cylinder group of an engine during a cold-start and flowing coolant to a second region of cylinder head coolant jacket corresponding to a second, active cylinder group while not flowing coolant to a first region corresponding to the first cylinder group, and where the first and second regions are fluidly sealed from each other. In this way, coolant flows to only regions of the cylinder head corresponding to active cylinders.
As one example, coolant is stagnated in an engine block coolant jacket, where the coolant is in contact with active and inactive cylinders. Therefore, the only flowing coolant flows through the second region of the cylinder head associated with the active cylinders. As the temperature of the coolant increases, the coolant may be mixed with coolant from the engine block in a coolant circuit, enabling more rapid warm-up of the cylinders (active and inactive). Once the cylinders are heated to a desired temperature, coolant may flow to all portions of the cylinder head such that heads of the deactivated cylinders may reach the desired temperature, thereby reducing emissions upon activation of the deactivated cylinders. This allows more rapid warming of an engine along with a catalyst reaching a light off temperature more rapidly.
It should be noted that the features and measures presented individually in the following description can be combined in any technically feasible manner and thus give rise to further embodiments of the present disclosure. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.